Numerous medical conditions are caused by insufficient blood flow to certain tissues. For example, angina and myocardial infarction are caused by insufficient blood flow to cardiac muscle, and ischemic stroke is caused by insufficient blood flow to the brain. Renal failure or hypertension is caused by insufficient blood flow to the kidneys. Claudication results from poor circulation of blood in the leg arteries, typically caused by atherosclerosis as a result of smoking, diabetes, or high cholesterol. In some cases, particularly in diabetes, poor blood circulation in the leg results in amputation. Erectile dysfunction is sometimes caused by insufficient blood flow in the arteries supplying blood to the penis. Retinal vessel occlusion (retinal artery or vein occlusion) often results in vision loss.
Heart failure is a chronic cardiac condition characterized by a deficiency in the ability of the heart to pump blood. Decreased cardiac output to the systemic circulation typically increases venous blood pressure, which often leads to blood backing up in the lungs. Low cardiac output also results in decreased blood perfusion to organs, such as the liver, kidney, brain, and heart itself. Over time, the effects of heart failure contribute to a worsening of the condition. Reduced blood supply to the heart causes less effective contraction of the heart. At the same time, higher venous blood pressure increases the heart preload. To compensate, the heart attempts to increase output by increasing muscle strength, which leads to myocardial hypertrophy (enlargement of the heart with thickening and stiffening of the heart wall). These conditions in turn lead to reduced cardiac output, resulting in a vicious cycle.
There are primarily two types of heart failure, systolic heart failure and diastolic heart failure. Systolic heart failure is characterized by a deficiency in systolic heart function, which causes insufficient expulsion of blood during systole. Diastolic heart failure is characterized by a deficiency in diastolic heart function, which causes insufficient ventricular filling during diastole.
Counterpulsation is a technique for assisting the circulation by decreasing the afterload of the left ventricle and augmenting the diastolic pressure. Devices for achieving counterpulsation include intra-aortic balloons, pumping devices implantable in the chest, and external devices that apply a negative pressure to the lower extremities during cardiac systole. Counterpulsation devices are typically synchronized with a patient's cardiac cycle to apply pressure to blood vessels of the patient during diastole, and to remove the applied pressure immediately prior to systole, so as to increase stroke volume by decreasing afterload, to reduce heart workload, and to maintain or increase coronary perfusion.
Counterpulsation techniques have been studied since the mid-1950s. Birtwell WC et al., in “The evolution of counterpulsation techniques,” Med. Instrum. 10:217-223 (1976), which is incorporated herein by reference, review the history of various counterpulsation techniques. Clauss RH et al., in “Assisted Circulation: 1. The Arterial Counterpulsator,” Journal of Thoracic and Cardiovascular Surgery 41:447 (1961), which is incorporated herein by reference, describe a pump placed on the arterial side of the circulation and used to alter the pressure of the left intraventricular aortic and arterial pulses. Unger F et al., in “The Windkesselventricle with guiding balloon as a new approach to assisted circulation,” Med. Instrum. 10:256-259 (1976), which is incorporated herein by reference, describe the implantation of balloons in aortas of dogs and a method for pneumatically driving the balloons synchronously with electrocardiogram (ECG) measurements, so as to increase hemodynamic efficiency.
Externally-applied counterpulsation devices are described, for example, in U.S. Pat. Nos. 5,554,103 and 5,997,540 to Zheng et al., and U.S. Pat. No. 3,866,604 to Curless et al., all of which are incorporated herein by reference. U.S. Pat. No. 5,514,079 to Dillon, which is incorporated herein by reference, describes techniques for improving circulation by applying external positive regional pressure on an extremity synchronously with the patient's heartbeat. An adjustable timing cycle is initiated at the QRS complex of the arterial pulse cycle. US Patent Application Publication 2002/0173735 to Lewis, which is incorporated herein by reference, describes a medical device for non-invasive counterpulsation treatment of heart disease and circulatory disorders through external cardiac assistance. The device comprises cuffs which are affixed on a patient's lower body and extremities, and which constrict by electromechanical activation, thereby augmenting blood pressure for treatment purposes.
PCT Publication WO 02/24254 to Khaghani et al., which is incorporated herein by reference, describes a blood circulation assistance device for location around a blood conduit. The device comprises an inflatable bladder for compressing the blood conduit to provide counterpulsation, and a pump for contracting and expanding the bladder. The pump expands the bladder at diastole, as determined by monitoring the cardiac cycle. An outer cuff surrounds the bladder in order to provide an outer limiting extent to the movement of the bladder.
U.S. Pat. No. 4,938,766 to Jarvik, which is incorporated herein by reference, describes implantable prosthetic devices and methods of use for increasing blood flow by increasing arterial compliance and reducing the magnitude of the pressure pulsations in the arterial system, and to increase perfusion of specific organs in order to overcome the deleterious effects of cardiovascular disease.
U.S. Pat. No. 6,030,336 to Franchi, which is incorporated herein by reference, describes a pump comprising variable volume means inserted in an artery, in particular, the descending aorta, enabling the volume through which the blood flows in this location to be modified cyclically and in a controlled manner. The device comprises a deformable enclosure in fluid communication with the variable volume. The variable volume and a spring coil urge the deformable enclosure against an increase of volume resulting from a pressure increase in the variable volume, and in the corresponding enclosure, so as to produce additional elastance for the artery during the heart cycle. In addition, an electric motor can control the deformable enclosure to increase or decrease its volume, and can exert its force in addition to or in subtraction from the force of the spring coil during the systolic and diastolic phases of the heart cycle.
U.S. Pat. No. 6,450,942 and European Patent Application 1 078 649 A1 to Lapanashvili et al., which are incorporated herein by reference, describe a technique for reducing heart load by measuring heart rhythm, and producing pressure pulsations in the peripheral vascular system in synchronization with the heart rhythm in a counterpulsation mode, so as to reduce pulse rate and/or systolic pressure, and thereby heart load.
U.S. Pat. Nos. 6,200,260, 6,299,575, and 6,428,464 to Bolling, and U.S. Pat. Nos. 6,387,037 and 6,390,969 to Boiling et al., all of which are incorporated herein by reference, describe an extracardiac pumping system comprising a pump implanted subcutaneously at a patient's groin. The pump draws blood from the patient's femoral artery and discharges blood to an artery that stems from the patient's aortic arch. The pump may be operated continuously or in a pulsatile fashion, synchronous with the patient's heart, thereby potentially reducing the pumping load on the heart.
U.S. Pat. No. 6,132,363 to Freed et al., which is incorporated herein by reference, describes a left ventricular-assist device comprising an inflatable bladder sutured into the wall of the descending thoracic aorta, a percutaneous access device (PAD) implanted in a hypogastric region of the patient and in fluid communication with the bladder, and a drive unit connectable through the PAD for selectively inflating and deflating the bladder.
US Patent Application Publication 2002/0151761 to Viole et al., which is incorporated herein by reference, describes an intravascular extracardiac system, comprising a pump with inflow and outflow conduits that are implanted intravascularly through a non-primary vessel, and positioned within the patient's vasculature. The pump is configured to be operated continuously or in a pulsatile fashion, synchronously with the patient's heart, thereby potentially reducing the afterload of the heart.
U.S. Pat. No. 3,585,983 to Kantrowitz et al. which is incorporated herein by reference, describes an intra-arterial cardiac-assist device having a balloon which is inflated periodically for diastolic augmentation. U.S. Pat. No. 4,630,597 to Kantrowitz et al., which is incorporated herein by reference, describes a dynamic aortic patch that is permanently surgically implanted in the wall of the aorta to augment the pumping action of the heart. The patch comprises an elongate semi-rigid shell member having a concave inner surface and a flexible membrane integrally bonded to the outer surface of the shell to define an inflatable and deflatable chamber between the concave inner surface and the membrane.
U.S. Pat. No. 4,240,409 to Robinson et al., which is incorporated herein by reference, describes a device for mechanically assisting circulation of blood in a patient for periods of up to two weeks until the patient's heart strengthens sufficiently to take over the full workload. The circulatory assist device includes a valveless pump with a flexible bladder, a pneumatic driver for applying pressure pulses to the bladder, and a single flexible conduit for conveying blood between the patient and the pump. In use, the pump and driver are mounted external to the patient's body and the flexible conduit is connected to the pump and in end-to-side relationship with a major blood vessel on that side of the heart, either right or left, which is in need of support.
U.S. Pat. No. 6,406,422 to Landesberg, which is incorporated herein by reference, describes a ventricular-assist system that utilizes an intraventricular device with a limited volume. The device is expanded at a critical time, for a critical duration, and with a volume change course such that it assists the pumping action of the heart without inducing stretching of the ventricular wall.
US Patent Application Publication 2002/0173693 to Landesberg, which is incorporated herein by reference, describes a system for assisting a failing ventricle, which utilizes a single blood displacement chamber and a single cannula. The cannula is inserted into the failing ventricle cavity and is connected to a blood displacement actuator. The device is described as producing blood displacement at a critical time for a critical duration and with blood flow time course such that it improves the systolic function of the heart, augments cardiac output, and increases the generated pressure. The device is also described as improving diastolic function by increasing the ventricle compliance and imposing rapid relaxation of the ventricle wall. The device is described as providing additional external work without deteriorating the mechanical function of the failing ventricle, moreover it is described as decreasing the energy consumption of the failing heart and improving coronary perfusion. Consequently, the device is described as improving the balance between the energy supply (coronary perfusion) to the ventricle wall and the mechanical demands, and to thereby allow recovery of the failing heart.
U.S. Pat. Nos. 6,673,043 and 6,511,413, also to Landesberg, describe related techniques to those described in the above-cited US Patent Application Publication 2002/0173693. These patents are incorporated herein by reference, as well.
U.S. Pat. No. 6,572,652 to Shaknovich, which is incorporated herein by reference, describes techniques for implanting a prosthetic valve in the pulmonary vein, in order to decrease or prevent an increase in pulmonary venous pressure. Expandable as well as fixed-dimension non-expandable pulmonary vein prosthetic valves for implantation by a variety of surgical and percutaneous procedures are described.
PCT Publication WO 98/57599 to Camilli, which is incorporated herein by reference, describes an implantable valve for use in blood vessels, particularly veins, more particularly venous confluences. The valve comprises a first supporting element in the shape of a bent body or of a cut sheet, and a second operative element in the shape of a leaflet, the two elements being joined one to another or the second one being integral with the first one. The valve is provided with anchor means and grip means to prevent longitudinal slipping when the valve is inserted in the blood vessel.
U.S. Pat. No. 6,299,637 to Shaolian et al., which is incorporated herein by reference, describes a self-expandable prosthetic venous valve, such as for implantation in the deep veins of the leg. The valve is mounted in a support structure, such as a self-expandable tubular wire cage.
US Patent Application Publication 2002/0103413 to Bugge et al., which is incorporated herein by reference, describes an implanted device for utilizing at least a part of the hydraulic energy generated by the heart to power various apparatus. The device typically includes a hydraulic motor powered by pressurized blood, which converts hydraulic energy into mechanical or electrical energy. The device typically stores the energy, and uses the stored energy to power an executing device, such as a pump or an electric motor. For some applications, the hydraulic motor is connected directly to one or more ventricles of the heart. Numerous embodiments of the device are described. For example, in one embodiment, the hydraulic motor is arranged as a unidirectionally acting pressure box in the form of two bellows connected in series, and with different cross-sectional areas resulting in the device's working as a differential piston. The bellows expand longitudinally against a return spring. Between the bellows is arranged a pusher plate having a valve that opens during diastole. A second valve is arranged at an opening of the smaller bellows for emptying the device. This valve opens during systole, at the same time as the return spring is compressed. In another embodiment, which is not described as having any valves, a counterpulsator includes the hydraulic motor and a pump, arranged as concentric bellows which are interconnected by a common pusher plate located within each other.
U.S. Pat. No. 4,527,549 to Gabbay, which is incorporated herein by reference, describes techniques for providing improved cardiac assist by the use of a intraaortic balloon. A single small balloon is placed in the ascending aorta close to the aortic valve, such placement being described as effective for producing a substantially stronger augmentation of heart action than with the use of a longer balloon normally placed, for example, in the descending aorta. Multiple small balloons positioned in the aortic arch, with or without a large balloon in the descending aorta, can be used to provide even stronger coronary flows.
U.S. Pat. No. 6,730,118 to Spenser et al., which is incorporated herein by reference, describes a valve prosthesis device suitable for implantation in body ducts. The device comprises a support stent, comprised of a deployable construction adapted to be initially crimped in a narrow configuration suitable for catheterization through the body duct to a target location and adapted to be deployed by exerting substantially radial forces from within by means of a deployment device to a deployed state in the target location, and a valve assembly comprising a flexible conduit having an inlet end and an outlet, made of pliant material attached to the support beams providing collapsible slack portions of the conduit at the outlet. The support stent is provided with a plurality of longitudinally rigid support beams of fixed length. When flow is allowed to pass through the valve prosthesis device from the inlet to the outlet, the valve assembly is kept in an open position, whereas a reverse flow is prevented as the collapsible slack portions of the valve assembly collapse inwardly providing blockage to the reverse flow.